The three Trump campaign associates headlining Monday’s news have been known quantities to Senate investigators investigating Russian efforts to interfere in the 2016 election. 

But the unsealing of a court filing showing that former campaign foreign policy adviser George Papadopoulos had already pleaded guilty to making false statements to the FBI and is a cooperating witness in the investigation led by special counsel Robert S. Mueller III probably explains why he has been elusive.

According to the court filings unsealed Monday, Papadopoulos was arrested July 27 at Dulles International Airport. He pleaded guilty earlier this month.

On Oct. 20, BuzzFeed reported that Senate Intelligence Chairman Richard M. Burr of North Carolina wanted to have Papadopoulos speak to the committee, describing him as a “person of interest.”

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In the same report, the panel’s vice chairman, Virginia Democrat Mark Warner, said Papadopoulos was proving hard to connect with.

“He is not often in the country,” said Warner.

That could be an indication that, in trying to figure out who is cooperating with Mueller, the focus should be on those not coming to Capitol Hill to speak with congressional investigators, particularly if they want to avoid inadvertent disclosure of sealed grand jury proceedings or even plea deals.

Paul Manafort, the former Trump campaign chairman who surrendered to the FBI on Monday morning on a host of charges including tax evasion, did speak with Senate Intelligence staff back in July, according to numerous reports.

“Paul Manafort met this morning, by previous agreement, with the bipartisan staff of the Senate Intelligence Committee and answered their questions fully,” Manafort spokesman Jason Maloni told reporters at the time.

The New York Times reported that during the discussion with the staff at a Washington law firm, Manafort provided notes from the Trump Tower meeting with a Russian lawyer in June 2016 that was apparently designed to transfer information harmful to Hillary Clinton, then the presumptive Democratic nominee for president.

It was not immediately clear whether the other individual whose indictment was unsealed Monday, Rick Gates, has already spoken with  Senate Intelligence. An committee aide declined Monday to say one way or the other.

Among other key associates to President Donald Trump or his campaign who have been publicly revealed to have met with Senate Intelligence staff are counsel Michael Cohen, Donald Trump Jr. and foreign policy adviser Carter Page.

Jared Kushner, Trump’s son-in-law and a senior adviser, also met with Intelligence staff, telling the panel in a July statement that he did not collude with Russian agents.

Unlike many individuals involved in the investigation, Kushner made a very public show of his appearance and apparent willingness to cooperate with Burr and Warner in July.

“I had no improper contacts” during the campaign and transition period, Kushner said, adding, “I have not relied on Russian funds for my business.”

Kushner’s mid-summer appearance in the White House driveway turned out to be just four days before Papadopoulos would be picked up at Dulles.

Joe Williams contributed to this report.